Dispersal of flammable materials

ABSTRACT

Apparatus for the safe dispersal of potentially dangerous concentrations of flammable vapors which are heavier than air comprising a solid vertical barrier at ground level and means associated with the solid barrier for ejecting jets of steam at high velocity.

United States Patent Cude et al. May 13, 19 75 DISPERSAL OF FLAMMABLEMATERIALS [56] References Cited [75] Inventors: Arthur Leslie Cude;Henry George UNITED STATES PATENTS Simpson, both of Stockton-on-Tees,212,719 2/1879 Mansfield 239/202 England 789,588 5/1905 Case 239/202802,772 10/1905 McCoy 239/202 [73] Assignee: lmperlal ChemicalIndustries Limited, London, England [22] Filed; A 20, 1973 PrimaryExaminer-Lloyd L. King Attorney, Agent, or Firm-Cushman, Darby & [21]App]. No.. 389,540 Cushman Related US. Application Data [62] Division ofSer. No. 145,714, May 21, 197].

[57] ABSTRACT [30] Foreign Application Priority Data Apparatus for thesafe dispersal of potentially danger- May 27, 1970 United Kingdom25528/70 011s concentrations of flammable vapors which are heavier thanair comprising a solid vertical barrier at 52 U.S. Cl 169/60; 239/202ground level and means a i t with the solid bar- 51 Int. Cl. A62c 3/00rier for ejecting j of steam at high velocity- [58] Field of Search239/208, 209, 200, 202,

6 Claims, 1 Drawing Figure 1 DISPERSAL OF FLAMMABLE MATERIALS This is adivision of application Ser. No. 145,714,

' fluids it is clearly desirable to prevent accidental release of thefluid into the atmosphere. Equipment which is to contain the flammaablematerial is designed specially to prevent such accidental release andoperation of the equipment is also laid down with this object in view.However, on occasion leakage and spillage of flammable material mayoccur despite the precautions taken to prevent the'accidental release.When release occurs a cloud of heavy vapour may be formed which iscapable of travelling considerable distances over the ground inflammable concentrations and which may be ignited by a source ofignition some hundreds of feet from the point of release. This hazard ismost apparent in the case of liquefied gases, but it applies equallywell to materials which are liquid under ambient conditions, when theyare processed or handled at elevated temperatures.

The invention is particularly applicable to flammable fluids which areprocessed, handled or stored at a temperature above their atmosphericboiling point. In designing plant for these purposes it is the aim toarrange the plant equipment so that there is a sufficient distancebetween potential sources of leakage or spillage and fixed sources ofignition to allow any escape of flammable vapour to disperse safelybefore the cloud of vapour reaches a source of ignition.

Nevertheless there are circumstances in which a particular plant areamay contain a relatively large number of potential sources of leakage orspillage, or in which the provision of an adequate safe distance betweenthe source of a leakage or spillage and a source of ignition isimpracticable. The chances of a fire and explosion resulting from anaccidental release of fluid may then be unacceptably high. We have nowdevised a method and equipment for the safe dispersal of concentrationsof flammable, heavier than air vapours in such circumstances.Accordingly, the present invention is a method for dispersing flammable,heavier than air vapour which comprises restraining the horizontaladvance of the vapour and, by means of turbulent steam jets, entrainingthe vapour together with sufficient air to reduce the concentration ofvapour below its lower flammability limit.

Flammable vapours which can be dispersed by the method of the presentinvention include gases, for example ethylene, and the vapours ofliquefied gases, for example liquefied petroleum gas (LPG), and ofliquids, for example petrol.

Although the method will disperse a moving cloud of vapour which has anarrow front, it is preferred to promote spreading of the cloud to awide front, for example while restraining the horizontal advance of thevapour, since the entrainment together with air in the steam jets isthen made easier.

The present invention also comprises equipment for dispersing a cloud offlammable vapour which comprises a solid barrier at ground level and asteam jet system associated with the solid barrier to disperse thevapour cloud by entrainment of the vapour with air.

The solid barrier is preferably a firewall which may be made of solidbrick but which may-also be made of I other materials which allow easybuilding and dismantling of the wall, for example, precast concretepanels and ribbed aluminium sheeting panels. Conveniently the wall isvertical but it may also be inclined away from the vertical, forexample, a bund wall, provided that it retardsadvance of the vapour.

Spacing of the solid barrier from the potential source of leakage orspillage may be governed by the proximity of sources of ignition but ifpossible, it is desirable to allow the cloud of vapour to broaden itsfront before meeting the wall. Where circumstances allow, a suitablespacing of the solid barrier from the potential source of leakage orspillage is 9 to 14 metres, preferably 11 to 13 metres. This spacing inparticular is suitable where ethylene is the vapour to be dispersed Thesteam jet system is preferably a pipe, or'pipes,

perforated with substantially circular holes and supplied with steamunder pressure.

' The perforated pipe, or pipes, may be positioned on top of the solidbarrier or, relative to the source of leakage or spillage, behind or infront of the solid barrier provided always that the relative positioningof solid barrier and the pipe allows substantially no'vapour to evadethe steam jet system. A preferred arrangement is to position the pipelevel with and adjacent to the top of a vertical wall. The pipe may reston top of the solid barrier or may be level with or below the level ofthe top of the barrier.

The length of the perforated pipe is preferably at least as great as thedistance between the potential source of escape and the solid barrier onwhich it is placed. Preferably the pipe is long enough to surround thepotential source of escape.

Preferably the jets in the perforated pipe are directed upwards so thatin operation, vapour reaching the solid barrier and steam jet system isentrained in the jets of steam together with a much larger quantity ofair. It is preferred for the steam to issue at at least sonic velocityfrom the holes in the perforated pipe or pipes.

To allay spark discharge of static electricity generated by the steampassing through the holes in the perforated pipe it is desirable toensure that the steelwork of the steam jet system and all othersteelwork and electrically conducting material in the vicinity of thesteam jets is earthed.

Conveniently, vapour detectors are provided between the potential sourceof leakage or spillage and the solid barrier to detect and give warningof the presence of flammable vapour. Preferably, the detectors alsoprovide an audible and/or visible signal which, optionally, actuates thesteam jet system so that dispersal of the vapour commences as soon aspossible after its presence is detected.

One embodiment of the invention will now be described with reference tothe accompanying drawing which is a diagrammatic view in perspective.

The equipment comprises a wall 1 made of precast concrete panels and 1.5metre high, spaced about 12 metres from a potential source of escape ofethylene from an olefmes plant 2. A perforated pipe 3 having i-inchdiameter holes 4 spaced 6 inches apart was mounted level with the top ofthe wall 1 to provide a steam curtain 3O mitres long. The jets weredirected vertically upward. Vapour detectors 5 were positioned betweenthe plant 2 and the wall 1 to detect and give warning of the presence offlammable vapour.

A vapour escape of ethylene at a rate of 7.2 kg/s. was found to requirea distance of 88 metres from the escape point for safe dispersal usingnatural air movementat a wind speed of 2.2 metres/second.

A similar escape in the same air conditions was safely dispersed in 28metres from the escape point using the wall and steam curtainhereinbefore described. The initial velocity of the steam jets was ofthe order of 425 metres/second and the height of the steam curtainformed was 24 metres.

We claim:

1. Equipment for dispersing a cloud of flammable vapour which comprisesa solid vertical barrier at ground level and spaced from a potentialsource of said flammable vapour, means associated with the solid barrierfor ejecting jets of steam at a high velocity upward from the ground,said means comprising at least one pipe of a length at least as great asthe distance between the potential source of flammable vapour and thesolid barrier, thereby dispersing the vapour cloud by entrainment of thevapour with air, vapour detectors positioned between the potentialsource of flammable vapour and the solid barrier and actuation means forthe steam jet system responsive to a signal from the detectors.

2. Equipment as claimed in claim 1 wherein the solid barrier is verticaland is made from a material selected from solid brick, precast concretepanels and ribbed aluminium sheeting panels.

3. Equipment as claimed in claim 1 wherein the spacing of the solidbarrier from the potential source of flammable vapour is 9 to 14 metres.

4. Equipment as claimed in claim 1 wherein the means for ejecting jetsof steam is a pipe or pipes perforated with substantially circularholes.

5. Equipment as claimed in claim 4 wherein the perforated pipe or pipesare positioned on top of the solid barrier.

6. Equipment as claimed in claim 1 which comprises a solid verticalbarrier made of solid brick, precast concrete panels or ribbed aluminiumsheeting panels and spaced at a distance of 9 to 14 metres from thepotential source of flammable vapour, a steam jet system consisting of apipe or pipes perforated with substantially circular holes positioned onor adjacent to the top of the solid barrier, the steam jets beingdirected upwards, vapour detectors positioned between the potentialsource of flammable vapour and the solid barrier and actuation means forthe steam jet system responsive to a signal from the detectors.

1. Equipment for dispersing a cloud of flammable vapour which comprisesa solid vertical barrier at ground level and spaced from a potentialsource of said flammable vapour, means associated with the solid barrierfor ejecting jets of steam at a high velocity upward from the ground,said means comprising at least one pipe of a length at least as great asthe distance between the potential source of flammable vapour and thesolid barrier, thereby dispersing the vapour cloud by entrainment of thevapour with air, vapour detectors positioned between the potentialsource of flammable vapour and the solid barrier and actuation means forthe steam jet system responsive to a signal from the detectors. 2.Equipment as claimed in claim 1 wherein the solid barrier is verticaland is made from a material selected from solid brick, precast concretepanels and ribbed aluminium sheeting panels.
 3. Equipment as claimed inclaim 1 wherein the spacing of the solid barrier from the potentialsource of flammable vapour is 9 to 14 metres.
 4. Equipment as claimed inclaim 1 wherein the means for ejecting jets of steam is a pipe or pipesperforated with substantially circular holes.
 5. Equipment as claimed inclaim 4 wherein the perforated pipe or pipes are positioned on top ofthe solid barrier.
 6. Equipment as claimed in claim 1 which comprises asolid vertical barrier made of solid brick, precast concrete panels orribbed aluminium sheeting panels and spaced at a distance of 9 to 14metres from the potential source of flammable vapour, a steam jet systemconsisting of a pipe or pipes perforated with substantially circularholes positioned on or adjacent to the top of the solid barrier, thesteam jets being directed upwards, vapour detectors positioned betweenthe potential source of flammable vapour and the solid barrier andactuation means for the steam jet system responsive to a signal from thedetectors.